linux-kernel - [PATCH v3 12/17] drm/bridge: cdns-dsi: Adjust mode to negative syncs

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Message-Id: <20250414-cdns-dsi-impro-v3-12-4e52551d4f07@ideasonboard.com>
Date: Mon, 14 Apr 2025 14:11:21 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Jyri Sarha <jyri.sarha@....fi>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>, 
 Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Jayesh Choudhary <j-choudhary@...com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 linux-phy@...ts.infradead.org, Francesco Dolcini <francesco@...cini.it>, 
 Aradhya Bhatia <aradhya.bhatia@...ux.dev>, 
 Devarsh Thakkar <devarsht@...com>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Subject: [PATCH v3 12/17] drm/bridge: cdns-dsi: Adjust mode to negative
 syncs

The Cadence DSI requires negative syncs from the incoming video signal,
but at the moment that requirement is not expressed in any way. If the
crtc decides to use positive syncs, things break down.

Use the adjusted_mode in atomic_check to set the sync flags to negative
ones.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
---
 drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 319a6a9a6fe7..182845c54c3d 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -901,9 +901,13 @@ static int cdns_dsi_bridge_atomic_check(struct drm_bridge *bridge,
 	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
 	struct cdns_dsi *dsi = input_to_dsi(input);
 	struct cdns_dsi_bridge_state *dsi_state = to_cdns_dsi_bridge_state(bridge_state);
-	const struct drm_display_mode *adjusted_mode = &crtc_state->adjusted_mode;
+	struct drm_display_mode *adjusted_mode = &crtc_state->adjusted_mode;
 	struct cdns_dsi_cfg *dsi_cfg = &dsi_state->dsi_cfg;
 
+	/* cdns-dsi requires negative syncs */
+	adjusted_mode->flags &= ~(DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC);
+	adjusted_mode->flags |= DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC;
+
 	return cdns_dsi_check_conf(dsi, adjusted_mode, dsi_cfg);
 }
 

-- 
2.43.0